Known technologies relating to legged mobile robots, particularly to the legs of legged mobile robots, include, for example, that set out in Japanese Patent No. 3293952. This prior art configuration secures driving forces necessary for walking by installing electric motors for driving the knee joints at the thigh links, installing electric motors for driving the ankle joints at the shank links, and driving speed reducers installed coaxially with the joint axes through belts.
When a legged mobile robot is caused to move, particularly when it is caused to move at high speed, large inertial forces are produced at the legs. It is therefore preferable to lighten the weight of the legs, particularly the ground-contacting ends thereof (ends contacting the floor surface; i.e., the distal ends), so as to reduce the inertial forces occurring in the legs during moving. However, the aforesaid prior art leaves room for improvement in the point of inertial force reduction because the weight of the ground-contacting ends of the legs is increased owing to the installation of the electric motors for driving the ankle joints at the shank links and the installation of the speed reducers coaxially with the ankle joint axes.